buggin under the full moon 

1.Actin real real retarded with no sense of rationality or purpose.
2.Talkin real real stupid chit

1st fella: "I think that kid had way too much too drink".
2nd fella: "why do you say that?"
1st fella: "he goin apechit, talkin all kinds of smack to that girl and humpin on her leg like a horny dog or somethin".
2nd fella: "awwwwww chit, he buggin under the full moon now".

buggin under the full moon by LycanLeader November 4, 2006

underfell 

UnderFell is an Alternate Universe created by fans. The main idea of it is everyone is their cruel counterparts, and apparently only wear orange, black, and red.

UnderFell is my favourite AU!

underfell by DepressingVoice16 July 6, 2016

Underfell Papyrus 

The Edgy Angry Alternate Universe Counterpart To Papyrus. He's more popular than that cool skeleton and has all the girls, such as Akari.

Akari stopped as Underfell Papyrus loomed over her, an angry expression on his face as usual

Underfell Papyrus by Rainy Melai October 26, 2017

Undermullet 

A haristyle for the pubic region of a woman where the vaginal area is shaved and the anus area is wrought with hair... this hairstyle is definately "business" in the front while "partying" in the back. This occurs most often to women who pay the most attention to their frontside while neglecting their nether regions.

That chick has an undermullet

Undermullet by Bushwacker69 June 23, 2011

Underfell 

Overated

Underfell is a overrated sans au

Underfell by Whybeanstastelikepepsi? February 11, 2021

Underfell 

The edgy version of the hit classic game undertale which involves some changes to the story as flowey is kind in the story.

The human stays in the underground as the adopted child of the king in the true ending after defeating their final boss.

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Abby: Underfell has a sans with a gold tooth. No further infromation about it.
Sandy: Aw, that is very sad indeed.
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Underfell by Retardost December 13, 2021

underfilled 

something that is lacking - metaphorically and/or physically. (Term popularized by @thekatcurtis)

“This bag of chips is more air than chips - it’s UNDERFILLED!!”

underfilled by funwitfunny March 16, 2022